1. Field of the Invention
The present invention relates to a ceramic material, in particular to fluorite type ceramics for use in the preparation of ion and/or electronic conducting ceramic products, in particular for membranes useful in the separation of oxygen and oxygen containing gas mixture and for electrolytes in fuel cells and electrochemical reactors.
2. Description of the Related Art
Fluorite ceramic materials for use in oxygen transport membranes have the general formula: EQU A.sub.x B.sub.y O.sub.2-.delta.
where
x.ltoreq.1 and y.ltoreq.1 and -1&lt;.delta.&lt;1, and PA1 A is one or more metals selected from the group of Ti, PA1 Zr, Hf, Ce and Th, PA1 B is Sm plus at least one metal selected from the group 2a and 3b and other lanthanides. PA1 x.ltoreq.1 and y.ltoreq.1 and -1&lt;.delta.&lt;1, and A is one or more PA1 metals selected from the group of Ti, Zr, Hf, Ce and Th, PA1 B is at least two metals selected from the group 2a and 3b and other lanthanides.
Classical ceramic materials for oxygen conductors are based on zirconia doped with metal such as Y, Mg and Ca.
Other ceramic oxygen conductors are based on ceria doped with metals such as Y, Sm and Gd. These materials may exhibit mixed ionic and electronic conductivity depending on oxygen partial pressure. The ceria based materials have a higher conductivity than the zirconia based materials at temperatures below 1000.degree. C., which makes the ceria based ceramics useful for commercial oxygen separation, fuel cell applications and catalysts. However, prices for pure ceria and pure dopants are prohibitive for more wide-spread commercialization. Furthermore, the pure mixed oxides typically used may be very refractory and very difficult to sinter into dense ceramic components.